This invention relates to dielectric materials useful in the formation of circuit materials, circuits, and multi-layer circuits.
As used herein, a circuit material is an article used in the manufacture of circuits and multi-layer circuits, and includes circuit laminates, bond plies, resin coated conductive layers, and cover films. Circuit materials are formed from a dielectric material that can be a thermosetting or thermoplastic polymer. The polymers are often combined with fillers such as silica to adjust the dielectric or other properties of the polymer. The dielectric material in a bond ply, resin covered conductive layer, or cover film may be substantially non-flowable, i.e., it softens or flows during manufacture but not use of the circuit, whereas the dielectric material in a circuit laminate (i.e., a dielectric substrate) is designed to not soften or flow during manufacture or use of the circuit or multi-layer circuit. Dielectric substrate materials can be rigid dielectric materials, which may comprise a fibrous web and/or other forms of reinforcement, such as short or long fibers or fillers.
A circuit laminate is a type of circuit material that has a conductive layer fixedly bound to a dielectric substrate layer. Double clad laminates have two conductive layers, one on each side of the dielectric substrate. Patterning a conductive layer of a laminate, for example by etching, provides a circuit layer, and thus a circuit. Multi-layer circuits comprise a plurality of conductive layers, at least one of which contains a conductive wiring pattern. Typically, multi-layer circuits are formed by laminating one or more circuits together using bond plies, and, in some cases, resin coated conductive layers, in proper alignment using heat and/or pressure. The bond plies are used to provide adhesion between circuits and/or between a circuit and a conductive layer, or between two conductive layers. In place of a conductive layer bonded to a circuit with a bond ply, the multi-layer circuit may include a resin coated conductive layer bonded directly to the outer layer of a circuit. In such multi-layer structures, after lamination, known hole forming and plating technologies may be used to produce useful electrical pathways between conductive layers.
A variety of polymeric dielectric materials are presently used to form in circuit materials, including phenol-formaldehyde resins, epoxy resins and, and isoprene and butadiene-based resins. Current polymeric dielectric materials often themselves are not flame retardant, and may thus contain bromine-containing additives to achieve a UL 94 rating of V-0. Due to new legislation in, for example, Europe and Japan, there is a great interest in removing bromine-containing compounds from circuit materials. Unfortunately, substitution of the bromine-containing compounds with other flame retardance additives often requires the addition of large amounts of additive, which can be detrimental to the electrical properties of laminates made with the polymeric materials. There thus remains a need for flame retardant polymeric materials for use in circuit materials, circuits, and multi-layer circuits that have suitable electrical and thermal properties.